In the art of joining the adjacent end portions of two generally aligned concrete reinforcing bars or "rebars", it is known to use a tubular steel coupling body or sleeve which receives the end portions of the bars. The coupling sleeve is crimped or swaged with substantial force against the reinforcing bars with the aid of a hydraulically actuated press and die set, for example, as disclosed in U.S. Pat. No. 3,551,999 and No. 4,241,490. It is also known to form tapered or non-tapered threads on the end portions of each reinforcing bar, and to join the end portions together with a coupling sleeve having internal tapered or non-tapered threads, for example, as disclosed in U.S. Pat. No. 197,509 and No. 3,415,552.
In order to avoid the need for hydraulically actuated press, a hydraulic pump and power source and a crimping die set, or to avoid the threading operation and protection of the threaded end portions of the reinforcing bars, it is also known to use a tubular coupler sleeve with longitudinally spaced and radially extending screws. According to one coupler as disclosed in U.S. Pat. No. 4,666,326 and No. 5,046,878, each of the screws has a hex shaped outer end portion and a threaded inner portion integrally connected by a reduced neck portion. The screws are tightened through the coupling sleeve into the reinforcing bars until the torque is sufficient to shear the hexagonal head portions from the threaded inner portions at the neck portions generally flush with the outer surface of the sleeve. This tubular coupling sleeve is also provided with a pair of elongated racks or hardened strips with inwardly and outwardly projecting teeth, and the ends of the strips are welded to the coupling sleeve. It has also been proposed to inject an epoxy material into these coupling sleeves after the screws are tightened for further increasing the gripping strength of the coupler sleeve with the opposing end portions of the connected reinforcing bars.
The forming of threads on the end portions of the reinforcing bars and the protection of the threads during handling and shipping of the bars add significantly to the cost of the reinforcing bars. In addition, the forming of internal threads within the tubular coupling sleeve adds to the cost of the coupling sleeve. In regard to the above described coupler with inner strips having teeth, the use of longitudinally spaced special screws increases the cost of the coupling sleeve, and the cost of the sleeve is further increased by the cost of forming the internal hardened strips with teeth on opposite sides and the cost for welding the strips within the coupling sleeve. Also, during installation, the strips of teeth sometimes bind upon the reinforcing bars as they are being inserted. This difficulty creates additional field labor. Further, once the heads of the special screws have been sheared off there is no provision to loosen the screws to reposition the coupler if it has been misinstalled. Another problem with special screws is that if the screws are not precisely formed, they are sometimes unreliable because the heads do not shear off at the prescribed torque.
Another form of tubular coupling with longitudinally spaced radial screws is disclosed in U.S. Pat. No. 4,314,771. However, this coupling sleeve is designed for connecting the opposing end portions of rods or shafts which do not require a high strength connection of the rods or shafts, as is required when joining reinforcing bars.